Re: modifying nullfs

From:

Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>

Date:

Fri, 7 Sep 2012 09:30:49 -0700 (PDT)

Most nullfs VOP's are going to go directly to the underlying
filesystem and NOT run through nullfs itself.
In DragonFly we don't have to replicate the vnode infrastructure for
directory nodes in nullfs because we track { mp, vnode } instead of
just { vnode }. nullfs is basically only used to track the
mount structure. Our namecache code handles mount points via the
chaining within the mount structures and NOT via chaining within
directory vnodes.
In otherwords, in DragonFly a nullfs mount as just as good as the
underlying filesystem mount, with no added overhead to use it.
-Matt
Matthew Dillon
<dillon@backplane.com>